The present disclosure relates to a device and method for controlling the SOC and SOH of an entire battery pack system in which two or more battery packs are connected in parallel.
More particularly, the present disclosure relates to preventing a sudden change in the SOC and the SOH of an entire system of a battery pack in which two or more battery packs are connected in parallel, and using the entire system of the battery pack in a safe range.
In recent years, as demand for portable electronic products such as notebook computers, video cameras, and portable telephones is rapidly increased and development of batteries for storage, robots, and satellites for energy storage is accelerated, studies on high performance secondary batteries capable of repeating charge and discharge have been actively conducted.
There are currently commercialized secondary batteries including nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among them, the lithium secondary batteries receive a lot of spotlight due to its advantages of being free from charge and discharge, very low self-discharge rate, and high energy density because the memory effect hardly occurs compared with the nickel-based secondary battery.
On the other hand, as carbon energy is gradually depleted and environmental concerns are rising, demand for hybrid cars and electric vehicles is increasing worldwide, including the US, Europe, Japan, and Korea. Since these hybrid vehicles and electric vehicles use the charge and discharge energy of a battery pack to obtain the vehicle driving power, they are more fuel-efficient than the vehicles using only the engine and do not discharge or reduce pollutants. Therefore, they are getting good responses from many consumers. Therefore, more attention and research are focused on automotive batteries, which are key components of hybrid vehicles and electric vehicles.
Recently, energy storage technology such as smart grid system is also one of the most popular technologies. The smart grid system is an intelligent grid system that aims to increase the efficiency of power utilization through the interaction of power supply and consumption by integrating information and communication technology into the production, transportation and consumption process of electric power. One of the important components to build such a smart grid system is a battery pack that stores power.
In such a way, the battery is used in various fields. In recent years, a field where a battery is heavily used, such as an electric vehicle, a hybrid vehicle, and a smart grid system, often requires a large capacity. In order to increase the capacity of the battery pack, there may be a method of increasing the capacity of a single battery pack itself. However, in this case, there is a disadvantage that the capacity increase effect is not large and there is a physical restriction on the size expansion of the battery pack and there is inconvenience in management. Therefore, a method of constructing a high capacity battery system by connecting a plurality of battery packs in parallel is commonly used.
However, when the battery packs are connected in parallel as described above, if the state of charge (SOC) between the battery packs is different from each other, electrical sparks may occur. Especially, in the case of a lithium secondary battery which is widely used in recent years, since the discharge current is very high as compared with other batteries, when battery packs with a different SOC are connected in parallel, it is possible to damage the battery cells and various circuits included in the battery pack. Also, there is a concern that it is possible to reduce the safety of a user (installer) who connects the battery packs due to the occurrence of spark.
In addition, even after a plurality of battery packs are connected in parallel, there may be a case in which the storage capacity of the battery pack is increased or a part of the battery pack is damaged and needs to be replaced. At this time, one or more battery packs should be additionally connected to the plurality of battery packs connected in parallel. In this situation, the additional connected battery pack may have a different SOC from the battery packs connected in parallel. At this time, electrical sparks may be generated to cause a problem in safety of the user and also may cause a problem of damaging battery pack cells or various circuit components.